In order to provide future energy requirements, various thermochemical processes have been developed in recent times by means of which water is decomposed into hydrogen and oxygen as hydrogen is an environmentally satisfactory energy supply. Such processes have in general been described as multi-stop processes in which in particular inorganic metal compounds, e.g. of iron, magnesium or vanadium as well as, for example, halogen or sulphur are employed as adjuvants. Efforts are being made to convey these adjuvants through the various reaction stages in a closed cycle, although this is obviously not essential. All these processes are relatively expensive however and offer considerable technical problems, so that up to now, no industrial-scale realisation has been undertaken.